The present invention relates to a manufacturing method of a surface acoustic wave device, and particularly, to a manufacturing method of a surface acoustic wave device serving as a branching filter and the like in, for example, a mobile communications field to handle high frequencies of about several GHz.
Surface acoustic wave devices (SAW devices) utilizing surface acoustic waves that concentrate their energy only at the surfaces of crystalline substrates involve propagation velocities slower than electromagnetic waves by about 10xe2x88x925, and the devices can be downsized. Accordingly, they are recently applied to filters, oscillators, delay elements, and the like in broad fields including TVs, VTRs, and communications equipment. Among them, the mobile communications field, in particular, frequently uses mobile terminals, etc., employing the branching filters consisting of downsized surface acoustic wave devices.
The surface acoustic wave device has a piezoelectric substrate and two comb-teeth-shaped aluminum (Al) electrodes formed on the piezoelectric substrate and mating with each other. Surface acoustic waves propagating at the surface of the piezoelectric substrate are driven or detected by the Al electrodes. Conventionally, the surface acoustic wave device is manufactured by employing a magnetron sputtering method to form an Al film on a wafer-like piezoelectric substrate at a constant film-forming velocity and by employing a lithography technique and an etching technique to shape the Al film into comb-teeth patterns. Branching filters used for mobile terminals such as mobile telephones handle high frequencies of about several GHz, and therefore, the comb-teeth shapes of the Al electrodes must have high dimensional precision. In particular, the thickness and evenness of the comb-teeth-shaped Al electrodes must have a 0.1-nm-order accuracy.
The present invention is to solve the technical problems of the above-mentioned background technology, and an object of the present invention is to provide a manufacturing method of a surface acoustic wave device, capable of precisely controlling the thickness and in-wafer-plane evenness of a metal film.
To accomplish the object, the present invention is characterized to provide a manufacturing method of a surface acoustic wave device, including forming a metal film on a wafer-like piezoelectric substrate and selectively removing the metal film to form comb-teeth-shaped metal electrodes. To form the metal film on the piezoelectric substrate, the method forms a part of the metal film in two or more film-forming modes involving different in-wafer-plane film-forming-velocity distributions and forms the remaining part of the metal film in a fixed film-forming mode.